1. Field of the Invention
This invention relates generally to monitoring devices including sensors and detectors, and more particularly, to infrared sensors or imagers.
2. Description of the Related Art
Monitoring devices are used in many different applications. For example, detectors and sensors forming part of a monitoring system may be used for intrusion security and video surveillance. Other applications include, for example, fire detection and emergency response. The applications may be, for example, military, non-military, personal, etc. Different types of devices may be provided based on, for example, the particular application or system in which the device is to be used. For example, infrared (IR) imagers configured as thermal cameras may be used within these systems to detect temperature changes.
Different types of IR imagers are known and generally include a bolometer or microbolometer device to detect incident electromagnetic radiation. These bolometers are essentially resistive thermometers that need to maintain a certain total resistance for optimum signal and noise properties. Accordingly, a material with a large value of thermal coefficient of resistivity (TCR) is preferred to produce better IR sensing performance.
With respect to IR imagers, both cooled and uncooled systems are known. For example, IR imagers with bolometers may include cooling systems, such as cryogenic cooling systems, and are known for use typically in military applications. These devices are often complex and larger in size. Further, the cost of these cooled imagers is high. Uncooled systems with microbolometers are less expensive and smaller in design. However, these uncooled systems must typically include a lower resistivity bolometer film material because of the in-plane conduction mode design of these bolometers. The lower resistivity materials often have lower values of TCR when compared to similar, but higher resistivity materials. Increasing the thickness of the bolometer film to improve electrical conduction increases the thermal inertia/capacity of the sensing portion of the device, thereby reducing the overall performance of the imager. The quality, for example, imaging quality, of the cheaper uncooled systems is typically less than the quality of the more expensive cooled systems.